A power line communication device may use a line coupling circuit to exchange communication signals with a (power) line, e.g., a power line in an electrical distribution grid.
The coupling circuit aims at improving signal exchange at the frequency of the communication channel and may include a signal transformer for isolation and differential coupling together with an inductor and a capacitor (that is, an LC circuit) for facilitating a “tuned” signal coupling to the power line.
State-of-the-art power line communication solutions may be capable of switching from one communication frequency channel to another. The capability of tuning the line coupling circuit to different communication channels may thus represent an asset.
A way of providing such a capability may involve arranging a switch (e.g., an opto-switch or relay) in parallel to a tuning inductor.
Such an arrangement may turn out to be expensive. Also, the inductor may be typically placed on the “high-voltage” (that is, power line) side of the coupling transformer, thus dictating isolation constrains adding to the cost and complexity of the solution. In addition, the switch may produce an appreciable power loss (e.g., with a Ron value for an electronic switch such as a transistor of about 0.5-1 Ohm).
Moving the switch and the tuning inductor to the low-voltage side, where the power line communication device is located, has been proposed as a way to palliate such drawbacks.
When resorting to such a solution, the switch may still be expensive. Even without stringent isolation constraint, it may still be required to operate with a relatively large signal across it (e.g., 36-40 V peak-to-peak), with significant losses in the switch.